The beauty of the .300 WM (or any other large capacity magnum, for that matter) isn't so much that you can load light bullets hot, but that you can load heavy bullets to respectable velocities. Generally for big game hunting distances under 400 yards, the "hardest hitting" bullet in a given caliber will be the heaviest bullet that can be loaded to about 2,900-3,000 fps. Here's why, specifically for the .300 Winnie.
A 165 grain Ballistic Tip (or Partition, it doesn't really matter) can be launched at about 3,200 fps muzzle velocity. With a 250 yard zero, you are about 3.5" above line of sight at the highest point in the bullet's flight, and at 400 yards, you are about 13" low. Energy drops from 3751 ft-lbs at the muzzle to 2140 ft-lbs at 400 yards.
Now then, a 200 grain Partition with a m.v. of 2950 fps with a 250 yard zero will have a max height of 4" above line of sight, and at 400 yards will be 14.5" low. Energy drops from 3810 ft-lbs at the muzzle to 2200 ft-lbs at 400 yards.
Looking at the data, one might say, "The numbers are almost identical, what's the big deal?". That is true, but there is one thing that has been left out - sectional density. A .248 sd vs. 301 sd means that the 200 grain bullet will penetrate much deeper at any given distance. This is no big deal on a whitetail, for either (Partition) bullet will likely go completely through at the given distances, but for an elk or something of equally large size, especially with a less than perfect angle, it can make a large difference indeed.
The only time I use 165 grainers (actually 168 gr Hornadys) in my .300 WM is when I load it down to 3,000 fps for whitetails/pronghorns only. I don't trust the bullet's construction for impact velocities above 3,000 fps, which is why it's loaded down. If it's for something bigger and/or long (over 300 yard) shots, I go with 200 grain Partitions.
My .300 WM likes a max load of RE 22 under the 200 grain Partition. I have to seat my bullets about .12" off the lands due to magazine box constraints, so my max load is actually 2 grains higher than what is listed as "max" in the Nosler manual. Velocity is 2,952 fps, which is a bit under the max velocities in Nosler manual #4. I've reloaded the practice/testing cases eight times, and the primer pockets are still tight, so the pressure is fine. Interestingly enough, accuracy is quite good with the bullets this far off the lands. Looking at my records, the last five three shot groups with this load average 1.04".
Like Del mentioned, each rifle is an entire system unto itself, and some may get max velocities in their rifle 2 grains UNDER listed max in the manual. Start low, work up, and in order to know where you are pressure/velocity wise, you really NEED a chronograph, or access to a friend's.
Re 22 is my powder of choice in the .300 Winnie and 7mm Rem Mag. N165 is also a very good choice, as is 4831.